Variable intensity lamp



Aug. 28, 1962 Filed Jan. 8, 1959 J. V. RICHARDS VARIABLE INTENSITY LAMP3 Sheets-Sheet l Aug. 28, 1962 J. v. RICHARDS 3,051,869

VARIABLE INTENSITY LAMP Filed Jan. 8, 1959 3 Sheets-Sheet 2 FIGB refevence vouaqe 5 error vokmge 1962 .1. v. RICHARDS 3,051,869

VARIABLE INTENSITY LAMP Filed Jan. 8, 1959 3 Sheets-Sheet 5 FIG. 4

QYTOY voltage QVVF v M PR2 Ye{erence voLtage United States PatentOflfice 3,5l,8h9 Patented Aug. 28, 1962 3,051,869 VARHABLE INTENSITYLAMP James V. Richards, Webster, N.Y., assignor t Wilmot Castle Company,Rochester, N.Y., a corporation of New York Filed Jan. 8, 1959, Ser. No.785,730 6 Claims. (Cl. 315-156) The present invention relates to avariable intensitylamp and, more particularly, to an automaticallycontrolled variable intensity lamp for producing an illumination ofsubstantially constant intensity at a specified area despiteinterferences between the area and the lamp or other changes ofconditions affecting the illumination of the area. For instance, in anoperating room it is desirable that the operative site on a patientlying on an operating table have a substantially constant illuminationeven though the doctors and nurses cast shadows by coming between thelamp and the operative site or if there should be a failure of someother light source in the room contributing to the illumination of theoperative site.

Accordingly, an object of the invention is to provide a generallyimproved and more satisfactory variable intensity lamp for automaticallyproducing a substantially constant illumination of an area despitechanges in conditions affecting the illumination of the area.

Another object of this invention is to provide a new and improved lampfor automatically illuminating an opera-ting table with light ofsubstantially constant intensity despite physical interference by thedoctors and nurses between the table and lamp during the course of theoperation.

Yet another object is the provision of a new and improved automaticallycontrolled variable intensity lamp responsive to changes in illuminationon a particular area so as to vary in brightness accordingly andilluminate the area with light of substantially constant intensity.

Still another object is to provide a new and improved automaticallycontrolled variable intensity lamp responsive to changes in theintensity of reflected light from an operative site on a patient lyingon an operating table such as might occur by physical interference ofthe hospital personnel between the operative site and the lamp, so as toilluminate the operative site with light of substantially constantintensity despite these random interferences.

A further object is the provision of a new and improved variableintensity lamp which operates more economically to provide asubstantially constant level of illumination at a particular areadespite physical interferences between the area and the lamp and otherchanges in conditions affecting the illumination of the area.

A still further object is to provide a new and improved lamp for anoperating room for facilitating safer and better operations by providingan improved light source.

These and other desirable objects may be attained in the mannerdisclosed as an illustrative embodiment of the invention in thefollowing description and in the accompanying drawings forming a parthereof, in which:

FIG. 1 is a front elevational view of a variable intensity lampaccording to the present invention shown situated above an operatingtable carrying a patient, the rays from the lamp being indicated in fulllines and the reflected light rays being indicated in dashed lines;

FIG. 2 is a schematic of a preferred control system for operating thevariable intensity lamp;

FIG. 3 is a circuit diagram of a typical control system in accordancewith the schematic of FIG. 2 utilizing a direct current bias supply; and

FIG. 4 is a circuit diagram of a typical system in ac- 2. cordance withthe schematic of FIG. 2 utilizing an alternating current bias supply.

The same reference numerals throughout the several views indicate thesame parts.

In FIG. 1 is illustrated a variable intensity lamp 11 constructed inaccordance with the principles of the present invention. Although thelamp 11 has general utility wherever it is desired to maintain anillumination of substantially constant intensity in a particular area,it is particularly useful in hospital operating rooms as an overheadlight above an operating table. The description will therefore proceedwith reference to this preferred use. Accordingly, the lamp 11 is shownin FIG. 1 suspended by means not here depicted, above an operating table13 on which rests a patient 15 in prone position.

The variable intensity lamp 11 comprises a flanged reflector housing 17within which are mounted one or more individual lamp units 19, four suchunits being shown in this figure. The lamp units 19 produce light rays21 which, as shown by the full lines indicating their path, are directedupon an operative site 23 on the patient 15. The reflected rays from theoperative site 23, as indicated by the dash lines 25, are detected byone or more photoresponsive devices 27 mounted in the lamp housing 17,four such devices being illustrated in the preferred embodiment. Anappropriate electrical circuit is provided between the photoresponsivedevices 27 and the lamp units 19 for maintaining constant the amount ofreflected light detected by the photoresponsive devices 27. By thiscircuit, a decrease of light detected by the devices 27 initiates anappropriate mechanism for increasing the brightness or intensity ofillumination of the lamp units '19, whereby the amount of reflectedlight is correspondingly increased. Of course, a reverse action isdesirably taken when the amount of reflected light increases, that isthe intensity of illumination of the lamps is decreased until the amountof reflected light reaches a predetermined level. This increase ordecrease in reflected light may occur, for instance, if the doctors ornurses tending the patient 15 interpose their bodies between the lamp 11and the operative site 23, thus casting shadows upon the operative site.

A schematic of a typical system for varying the intensity ofillumination of the lamp units 19 so as to produce a substantiallyconstant amount of reflected light detected by the photoresponsivedevices 27 is shown in FIG. 2. This system is commonly known as a closedloop feedback control system. The photoresponsive device takes the formof a photoaresistor 27 which produces a voltage hereafter known as theerror voltage. This error voltage provides a first input to a summingnetwork X. A reference voltage provides a second input to the summingnetwork X and is derived from a potentiometer P. In the summing networkX, the error voltage is compared to the reference voltage, thedifferential output of the summing network becoming the input for amotor control amplifier A. The amplifier A produces a current flow inone or the other of the windings of a motor M connected in series withthe amplifier A and the summing network X. A v-ariac V having a wiperarm is actuated by the motor M to cause rotation of the wiper arm,whereby the voltage output of the variac V increases or decreasescorrespondingly. This output voltage is applied to the lamp 13 to varythe brightness of the lamp 19 to thereby increase or decrease theillumination of the operative site. The increase or decrease in thereflected light from the operative site is again detected by thephoto-resistor 27, producing a different error voltage which is againcompared with the reference voltage as described above. Thereafter thesystem operates in a manner already described to change the brightnessof the operating lamp 1?. Actually, the comparison of voltages is acontinu ous process and when the comparison is nearly equal, that is,when the differential voltage approaches a null, the amplifier A ceasesthe production of control signals and the system is in equilibrium. Thesystem is damped by the friction and time lag introduced by themotorvariac gearing, to prevent instability. The reference voltageproduced by the potentiometer P may be adjusted to produce apredetermined intensity of illumination at the operative site.

There are a number of specific circuits which may operate in accordancewith the schematic system of FIG. 2. Two of the many possible circuitswill be described, one operating from a direct current bias supply andthe other operating on an alternating current bias supply.

In the circuit of FIG. 3, a DC. supply voltage is provided in aconvenient manner such as by use of a battery B1. The series combinationof a photo-resistor PR1 and a resistor R11 are connected in parallelwith the battery B1 and a potentiometer R12. The Wiper on thepotentiometer R12 is adjusted to supply an appropriate tap-off voltagehereafter known as the reference voltage. To provide an error voltagedependent in magnitude on the resistance of the photo-resistor PR1, alead 31 is tapped between the photo-resistor PR1 and resistor R11.

The reference and error voltages are applied to a servo-amplifier havingconnections to the control Windings W1 and W2 of a reversible A.C.motor, the speed and direction of rotation of which is determined by theservoamplifier. It is to be understood, of course, that the reversiblemotor controls the position of the wiper of a variac in accordance withthe schematic of FIG. 2. The positive side of the winding W1 isconnected to the plate of a thyratron V1. The winding W1 is in serieswith a capacitor C1, and a rectifier X1 is in parallel with both, therectifier being conductive in the direction of the plate of thethyratron. In similar fashion, the positive side of the motor Winding W2is connected to the plate of a thyratron V2, and a capacitor C2 is inseries with the winding W2, both being in parallel with a rectifier X2conductive in the direction of the plate of the thyratron.

To provide a reference potential for the tubes V1 and V2, a battery B2is provided and a pair of potentiometers R5 and R6 are connected acrossits terminals. The voltage picked off of potentiometer R5 by its wiperis conducted through a resistance R3 to the shield grid of thyratron V1,and in similar fashion the voltage picked off of potentiometer R6 isconducted through a resistance R4 and impressed on the shield grid ofthyraton V2. The cathodes of the tubes V1 and V2 are referenced to theshield grids by being connected through resistances R9 and R10,respectively, to the positive terminal of the battery B2. Capacitors C3and C4 extend between the shield grid and cathode of the tubes V1 andV2, respectively.

The cathode potential of thyratron V1 is impressed through resistance R7and R2 on the control or signal grid of thyratron V2, the negative sideof the capacitor C1 being tapped into this electrical path between thetwo resistances. In similar fashion, the potential of the cathode oftube V2 is impressed on the control grid of the tube V1 throughresistances R8 and R1, the negative side of the capacitor C2 beingtapped into this circuit between the two resistances. The referencevoltage from the potentiometer R12 is applied to the cathode ofthyratron V1, whereas the error voltage dependent on the resistance ofthe photo-resistor PR1 is applied to the cathode of thyratron V2.

In considering the operation of the servoamplifier, it is to be notedthat the motor control windings W1 and W2 are wired into the circuit sothat the plate potentials at the thyratons V1 and V2 are in phase. Thus,when the error and reference voltages are equal, the cathodes of V1 andV2 are also at the same potential and an equilibrium condition exists.The lamps 19 powered by the variac therefore stay at a substantiallyconstant brightness. The potentiometer R12 may be adjusted to supply adesired reference voltage according to the level of illumination desiredat the operative site.

A change in the intensity and amount of reflected light from theoperative site 23 causes a change in the resist ance of thephotoresistor PR1 and as a result the error voltage increases ordecreases correspondingly. If the error voltage becomes more positivethan the reference voltage, then the control grid of V1 will becomerelatively more positive than its cathode. When the plate of V1 issufiiciently positive V1 will fire. When V1 conducts, current will flowin the circuit from the anode to the cathode, through R7 to C1, throughC1 and through W1 and back to the anode. When current flows through R7,the cathode end becomes more positive with respect to the capacitor end.Thus, whenever V1 fires, the control grid of V2, which is connected tothe capacitor end of R7 through resistor R2, experiences a suddenincrease in negative bias, preventing V2 from firing as long as V1 isconductive. As long as this cathode inbalance exists, V1 fires each halfcycle and V2 fires on neither half cycle, and the motor moves stepwisein the direction directed by Winding W1. The variac wiper thus moves toa new position to vary the voltage supplied to the lamp units 19 tochange correspondingly the illumination supplied to the operative site23. At the new position of equilibrium, the error voltage becomessubstantially equal to the reference voltage, the cathode balance isrestored and tubes V1 and V2 are again in equilibrium, holding thevariac wiper in substantially the same position.

Should the error voltage become more negative than the referencevoltage, tube V2 operates each half cycle in a manner similar to thatdescribed above, whereas tube V1 is driven to cut off by having therelatively negative potential of the capacitor end of R8 impressedthrough the resistance R1 on the control grid of V1. The control motormoves stepwise in a direction directed by winding W2 until a newcondition of equilibrium is attained.

A satisfactory servoamplifier has been constructed in which the variouscomponents have the following values: C1, C2=3 mfd.

C3, C4=0.01 mfd.

R1, R2=50K ohms R3, R4, R9, R10=150K ohms R7, R8 =500 ohms R11=100K ohmsR12=150K ohms V1, V2=2D21 or 2-D21W thyratron X1, X2=selenium rectifierW1, W2=control windings of a Barber Colman reversible A.C. control motorB1=15O volts direct current B2=6 volts direct current In FIG. 4, acircuit using an alternating current bias supply is illustrated andoperates in accordance with the schematic system of FIG. 2. Thealternating current supply is conventional ll0-120 volts, 60 cycles persecond. Connected across the A.C. supply is a phase matching transformer33 preferably having a 1:1 ratio. Across the output coil of thetransformer 33 is inserted a potentiometer R20 having a wiperfor-tapping off a desired voltage, hereafter called the referencevoltage. In parallel with the potentiometer R20 is the seriescombination of a resistance R21 and a photo-resistor PR2. A lead 35 istapped between these series resistors and taps off a voltage dependenton the resistance of the photo-resistor PR2, hereafter called the errorvoltage.

A reversible A.C. control motor is provided having a control winding W3having ends A and C. A center tap at point B of the winding W3 isconnected to the plate of a thyratron V3. The winding ends A and C,which are electrically 180 out of phase, are each connected to thecathode of the tube V3. A rectifier X3 is inserted between the end A andthe cathode and is conductive in the direction of the end A. Similarly arectifier X4 is inserted between the other winding end C and the cathodeand is conductive in the direction of end C. The shield grid of the tubeV3 is tied to the cathode and therefore has the same potential. Thecathode of the tube is connected to the wiper of the potentiometer R23and thus has the reference voltage impressed on it. The control grid ofthe tube is connected through a resistance R22 to the tap-off lead 35and thus has the error voltage applied to it. A by-pass resistor R23 isinserted between the cathode and control grid.

In the operation of the circuit of FIG. 4, the potentiometer is set togive the desired reference voltage according to the level ofillumination desired. [The control motor having the winding W3, ofcourse, operates a variac Wiper supplying power to a lamp unit 19. Whenthe reference and error voltages are equal or substantially equal, thecathode and control grid of the thyratron V3 are substantially at thesame potential and the tube does not fire.

The circuit operates in the following manner when the error voltage isnot equal to the reference voltage. As an example, let the potentiometerR20 be adjusted so that the wiper is electrically midway between pointsP1 and P2, these points being at the ends of potentiometer R20 as shownin FIG. 4. If the illumination is such that the resistance of thephoto-resistor PR2 has a resistance precisely equal to that ofresistance R21, there will be no potential difference between points P3and P4, point P3 being located at the wiper of potentiometer R20 andpoint P4 being located at the tap between lead 35 and the connectionbetween resistance R21 and potentiometer PR2.- However, if the amount oflight falling on PR2 decreases its resistance will increase and thepotential of point P4 will approach the potential of point P1. If atthis instant the AC. voltage across transformer 33 is such that PI ispositive, then P4 will become more positive than P3 and there will be aninstantaneous positive potential on the control grid of the thyratron.If at the same instant, end A of winding W3 is negative with respect tocenter tap B, tube V3 will fire, passing current from tap B to the anodeof V3, through the tube to the cathode, through rectifier X3, thence towinding end A and through the winding half AB back to mid-point B. Themotor will run in the direction controlled by winding half AB. Duringthe next half cycle, point P4 will swing negative with respect to P3and, although mid-point B will be positive with respect to end C, thetube will not fire because of the negative error signal on the controlgrid from point P4.

If the resistance of photo-resistor PR2 decreases, due to an increase inillumination, the polarity of point P4 approaches that of point P2resulting in a phase shift of the error signal with respect to the twohalves of winding W3. Thus, winding half OB will control the directionof rotation.

One can see that the motor operates every half cycle, until the errorand reference voltages are substantially equal, at which timeequilibrium is again established.

A circuit according to FIG. 4 which proves to be satisfactory has thefollowing values for its various components.

R21=100K ohms PR2=Clairex CL-402 photo-resistor R22=10OK ohms R23=1megohm V3=2D21W thyratron X3, X4=Federal IT & T 1004A rectifier As hasalready been mentioned, the particular circuits of FIGS. 3 and 4 and theschematic system of FIG. 2 are merely illustrative ways of regulatingthe intensity of illumination or the brightness of the lamp units 19 asa function of the intensity of reflected light falling on aphoto-resistor. In its broader aspects, the invention includes any lightsensitive detector or apparatus which produces a signal dependent on theintensity of illumination falling upon it, and any type of device orcircuit between the lamp and the light sensitive detector or apparatuswhich is capable of reacting to this signal to regulate the intensity ofillumination of the lamp in dependence thereon.

The preferred apparatus utilizing photo-resistors and a closed loopfeedback circuit between the photo-resistors and the lamp is a verysatisfactory arrangement because it operates automatically and adjustsquickly to keep the intensity of illumination at the operative site 23at a substantially constant level. Stated otherwise, the intensity ofreflected light striking the photo-resistor is maintained at asubstantially constant level. When using a lamp 11 according to thepresent invention, the operating personnel are able to perform a better,safer and quicker operation because the lighting is more constant anddependable. Because the illumination automatically increases whenshadows are cast on the operative site 23, there is no need to manuallyshift or otherwise regulate the lighting during the course of theoperation. The use of the lamp 11 furthermore is economical since theintensity of illumination is not kept at a needlessly high level inorder to provide suflicient illumination during times when shadows arecast or the illumination at the operative site is reduced for one reasonor another.

It is seen from the foregoing disclosure that the above mentionedobjects of the invention are well fulfilled. It is to be understood thatthe foregoing disclosure is given by Way of illustrative example only,rather than by way of limitation, and that without departing from theinvention, the details may be varied within the scope of the appendedclaims.

What is claimed is:

1. A variable intensity lamp for illuminating a particular area subjectto varying light reflecting properties com prising a lamp unit and aphoto responsive device for detecting the amount of light reflected fromthe area, means for producing an error voltage dependent in magnitude onthe amount of reflected light detected by said photo responsive device,means for producing a reference voltage dependent in magnitude on theamount of reflected light desired at the area, means for comparing saiderror and reference voltages, and means for utilizing the differentialbetween said error and reference voltages to vary the intensity ofillumination of said lamp unit to maintain a substantially constantamount of reflected light from said area to be detected by said photoresponsive device.

2. A variable intensity lamp for use in an operating room forilluminating an operative site, subject to varying light reflectingproperties, in order to produce a substantially constant amount ofreflected light, said lamp comprising a light producing means and aphoto responsive device for detecting the amount of light reflected fromthe operative site, and closed loop feedback system means for varyingthe intensity of illumination of said light producing means independence on the amount of reflected light detected by said photoresponsive device to maintain substantially constant the amount ofreflected light detected by said photo responsive device, whereby theamount of light reflected from the operative site is kept substantiallyconstant despite physical interferences by the operating personnelbetween the lamp and said operative site.

3. A construction as defined in claim 2, wherein said photo responsivedevice comprises a photo-resistor and said closed loop feedback systemmeans includes means for producing an error Voltage dependent on theresistance of said photo-resistor, means for producing a referencevoltage dependent on the amount of reflected light desired from theoperative site, means for comparing said reference and error voltages,and means for utilizing the difierence between said voltages to vary thepower supplied to said light producing means to vary the intensity ofsaid light producing means in proportion to the diflerential betweensaid voltages.

4. A variable intensity lamp for illuminating a particular area subjectto varying light reflecting properties, said lamp comprising lightproducing means and a photo responsive device, and means between saidlight producing means and photo responsive device for varying theintensity of illumination of said light producing means in dependence onthe amount of light reflected from the area detected by said photoresponsive device to maintain the amount of reflected light beingdetected at a substantially constant level.

5. A construction in accordance With claim 4 wherein said photoresponsive device is a photo resistor and said means between said lightproducing means and said photo responsive device is a feedback systemmeans.

6. A variable intensity lamp for illuminating a particular area subjectto varying light reflecting properties, comprising a light producingmeans and a photo responsive device for producing a signal dependent onthe amount of reflected light from the area detected by said photoresponsive device, means for producing a reference signal dependent onthe amount of reflected light desired from the area, and means forcomparing said signals and utilizing the diflerential to vary theintensity of illumination of said light producing means to maintain asubstantially constant amount of reflected light from the area.

References (Titer! in the file of this patent UNITED STATES PATENTS2,012,821 King Aug. 27, 1935 2,030,854 Calver Feb. 18, 1936 2,205,255Gulliksen June 18, 1940 2,232,373 D'orst Feb. 18, 1941 2,269,324 TurnerJan. 6, 1942 2,411,440 Le Page Nov. 19, 1946 2,477.646 Perlow Aug. 2,1949 2,573,554 Dwyer Oct. 30, 1951 2,823,301 Stevens Feb. 11, 19582,882,450 McCabe Apr. 14, 1959

